Black paint over spare body parts add extra android head that comes with the Caves of Androzani set.
The Android Rebel were androids used by Sharaz Jek for his guerrilla efforts on Androzani Minor. They were programmed to kill any humans they encountered who didn't have belts which produced specific frequencies of sound and had limited intelligence. They could also modified to look like specific individuals, allowing Jek to infiltrate enemy bases. These modified androids had more complex brains and the ability to see through walls. (TV: The Caves of Androzani)